The customer observed that changing items order in Relation List doesn't work on the latest (at the time of creating this ticket) Firefox. Google Chrome is not affected.

 Steps to reproduce:
1. Create a new CT with Content Relation (multiple) Field Type.
2. Create new content using this CT.
3. Add several (e.g. 3) content objects to the list.
4. Change the order of the first content to 4.

Result:
The first content does not go to the last position according to its order.

Expected result:
The first content should be ordered as the last.

Note:
Possible JS error (wasn't able to observe any in the console but could be a potential clue):

Error in Console: Permission denied to access property "nodeType".